Thermodynamic analysis and evaluation of a novel trans-critical CO2 power system incorporating partial condensation, sub-cooling, and recompression

Abstract

Trans-critical CO2 Rankine cycle (TRC) is a promising technology that converts heat into power generation with its safe and environment-friendly characteristics. However, the low critical temperature of CO2 restricts the practical application of TRC, which requires a relatively low temperature heat sink to ensure the CO2 condensation. In addition, the heat capacity mismatch between hot and cold CO2 streams in the recuperator restricts the performance improvement of traditional recuperative trans-critical CO2 Rankine cycle (RTRC). In this study, a novel partial condensation trans-critical CO2 recompression cycle (PCRC) is proposed to simultaneously address the issues of condensing difficulty and low performance. Thermodynamic analysis and optimization models for both PCRC and RTRC are formulated and a solution algorithm is developed. Case studies are explored to validate the superiority of PCRC over traditional RTRC in thermal efficiency and operation flexibility. Influence of key parameters on the PCRC performance is also investigated to reveal the improvement mechanism over RTRC. Furthermore, sensitivity analysis is carried out on the upper operation pressure, heat source parameter, and heat sink parameter of the PCRC to determine its operational flexibility.